During the handling of an imaging material, such as coating, drying, finishing, winding, rewinding, printing, projecting, and so on, the material surfaces are often damaged by contact friction with various equipment or as a result of contact between the front and back side of the imaging material. For example, scratches or abrasions can result on the emulsion and back side of a photographic material. These scratches or abrasion marks are visible during printing or projecting processes. This causes serious problems in the practical use of the films. In addition, when the contact friction is high, the imaging materials do not transport smoothly during the manufacturing process or in various exposure, processing, and projection machines. These transport problems may result in product waste. In recent years, the conditions under which the imaging materials are manufactured or utilized have become more severe, because their applications have been extended (for example, in an atmosphere of high humidity and high temperature) or because the methods for their preparation have been advanced (for example, high speed coating, high speed finishing and cutting, and fast processing). Under these conditions, the imaging materials are more easily damaged.
To lower the contact friction and improve the resistance to damage to surfaces, a lubricant or slipping agent is often used. Examples of the lubricants used for these purposes include silicone fluids as described in U.S. Pat. No. 3,489,567, and wax esters of high fatty acids or high fatty alcohols in U.S. Pat. No. 3,121,060. Problems are encountered in the use of these lubricants. For example, waxes such as Carnauba wax have been used to form the backing lubricant layer. However, they need to be coated from solvents such as propylene dichloride, which is on the EPA P/U highly hazardous list. Furthermore, waxes in most cases have to be applied as a separate layer, which requires an additional coating station and therefore increases product cost.
Silicone fluids are frequently used as lubricants, but, they are prone to transferring from one side of the imaging element to the other side when the element is stored or supplied in a wound roll form, such as a photographic film for amateur photography. In addition, since these silicone fluids are insoluble in water they must be dispersed with mechanical energy and, typically, in the presence of large amounts of surfactant, into aqueous coating compositions. This process results in coatings containing silicone fluids dispersed as fairly large droplets which may cause the dried coatings to be hazy in appearance. The large amounts of surfactant used to disperse the silicone fluids may be undesirable since they may cause the coating composition to foam and may compromise the physical properties (for example the barrier properties) of the dried layer.
Siloxane-containing polymers have been described for use in backing layers or slipping layers for imaging materials. U.S. Pat. No. 4,961,997 describes a backing layer for use in a thermal recording medium which comprises a cured product of a mixture of a silicone-modified polyurethane resin and a heat-resistant organic powder. The patent discloses that the backing layer may be applied from organic solvents such as paraffin solvents, aromatic solvents, ketones, alcohols, esters, and their mixtures. The patent does not teach or disclose backing layers applied from aqueous medium.
U.S. Pat. Nos. 4,910,087 and 4,942,212 describe heat-resistant layers for heat-sensitive recording elements in which the heat-resistant layers are made of a polyurethane resin containing a siloxane. These patents disclose applying such layers from organic solvent medium.
U.S. Pat. No. 5,330,840 describes polysiloxane containing polyurethane coatings for rollers and belts useful for toner fusing in electrophotography. The coatings were applied from an organic solvent such as tetrahydrofuran.
U.S. Pat. No. 5,451,495 describes a photographic element comprising a support, at least one light-sensitive silver halide containing layer and a layer comprising a crosslinked polymer having tertiary nitrogen atoms that are converted to quaternary amines. The polymer backbone moieties are polycondensation polymers such as polyurethanes and the crosslinking moieties are siloxanes. However, polymers containing quaternary amines are undesirable for photographic applications due to their propensity to interact with anionic filter dyes leading to possible dye stain after film processing. In addition, the layers were not described as being applied from aqueous medium.
Solvent-soluble siloxane-containing polyimides and polyesters for use in slipping layers for dye-donor elements in thermal dye transfer are described in U.S. Pat. Nos. 5,252,534 and 5,234,889, respectively. These slipping layers were described as being applied from organic solvent medium.
A foremost objective of the present invention is to provide an imaging element having a new surface protective layer composition which can be applied from an aqueous medium. The coating compositions used to form such a surface lubricant layer are stable with respect to manufacturing processes and are attractive from an environmental standpoint. The surface protective layer prepared has excellent lubricity.